CN113748086A - Method for refining a crude silicon melt using a particulate mediator - Google Patents

Method for refining a crude silicon melt using a particulate mediator Download PDF

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CN113748086A
CN113748086A CN201980095911.8A CN201980095911A CN113748086A CN 113748086 A CN113748086 A CN 113748086A CN 201980095911 A CN201980095911 A CN 201980095911A CN 113748086 A CN113748086 A CN 113748086A
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silicon
mediator
mass
refining
particulate
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CN113748086B (en
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K-H·里姆伯克
K·毛特纳
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Wacker Chemie AG
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/037—Purification
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/14—Pore volume

Abstract

The subject of the invention is a method for the oxidative refining of crude molten silicon in the production of industrial silicon, wherein the crude molten silicon is mixed during refining with a particulate mediator containing a minimum of 8 mass% of metallic silicon and at least one or more of the elements H, C, O, F, Cl, Ca, Fe and Al, the mediator being described by a characteristic number K having a value of 0.03 to 6mm‑1And calculated as follows:
Figure DDA0003327471960000011
wherein d is50,MIs the particle diameter (diameter) d at 50% of the cumulative distribution on the particle diameter distribution curve of the mediator50,Med[mm]And em,MIs the average effective porosity of the particulate mediator.

Description

Method for refining a crude silicon melt using a particulate mediator
The present invention relates to a method for the oxidative refining of crude molten silicon in the production of industrial silicon, wherein the crude molten silicon is mixed with a particulate mediator (particulate mediator) comprising metallic silicon.
The main applications of technical-grade silicon (technical silicon) are currently used in silicothermic operations, in metal extraction, and as a deoxidizer in steel making, where silicon is used as an alloy component of cast alloys of aluminum, copper, titanium and iron, and also as a raw material for chemical compounds.
Industrial grade silicon is commercially produced from quartz (SiO)2(ii) a Optionally further additions, e.g. iron-containing waste [ ferrosilicon]Or calcium carbide [ silico-calcium ]]) Produced by carbothermic reduction according to net reaction equation (1) in an electric furnace (arc reduction furnace) at high temperature (about 2000 ℃) and atmospheric pressure. The process is fully described in the standard work "Production of High Silicon Alloys" (A.Schei, J.K.tuset, H.Tveit, Production of High Silicon Alloys,1998, Tapir for lag, Trondheim).
SiO2+2C→Si(l)+2CO(g) (1)
During operation, the reactants, intermediates and products are present in various states of matter: solid state (C, SiC, SiO)2Si), liquid (Si, SiO)2) And gaseous (mainly CO, SiO). The carbon source used is generally a reducing mixture consisting of coke, petroleum coke, bituminous coal, charcoal and wood particles. The atmosphere prevailing in the furnace is a strongly reducing atmosphere, in particular consisting of SiO and CO. During operation, SiO2And C moves downward while SiO and CO flow upward. Forming an intermediate species according to equations (2) - (7) below:
SiO2+C→SiO+CO (2)
SiO+2C→SiC+CO (3)
SiO2+2SiC→3Si+2CO (4)
2SiO2+SiC→3SiO+CO (5)
SiO2+CO→SiO+CO2 (6)
2CO2+SiC→SiO+3CO (7)
silicon is mainly formed by the reaction shown in reaction (8).
SiO+SiC→2Si+CO (8)
Such high temperature operation requires extremely continuous conditions. The raw material and the liquid crude silicon are also intermittently charged and discharged, respectively. The draining is typically accomplished by draining the furnace and then transferring the liquid crude silicon (at a temperature of about 1600 to 1900 ℃) into a processing vessel.
The key factors are the quality of the product produced, as well as the economic aspects of the industrial operation (e.g., productivity and production costs). When metallurgical silicon is used for the production of chemical compounds such as chlorosilanes, the impurities contained in the silicon (for example boron in the form of volatile chlorides) are partly, although via intermediate purification stages, carried over into the respective end product (for example polycrystalline silicon, silicone) through a plurality of operating steps. However, depending on the field of application, these end products must meet very strict quality requirements (semiconductor/pharmaceutical/food/cosmetic industry). Therefore, high quality raw material, metallurgical silicon, is important for the production of these products on an industrial scale.
Is commonly used for SiO2The raw material and the electrode for carbothermic reduction of (2) contain various impurities. The liquid crude silicon is typically subjected to oxidative refining in the treatment vessel described above, since up to 5 mass% of impurities are still present in the crude product. In this field, it is customary to use reactive gas mixtures (e.g. Cl)2、O2、SiCl4Wet H2And CO2Or combinations thereof, typically diluted with an inert gas) and adding slag-forming additives (e.g., silica sand, limestone, quicklime, dolomite, fluorite, etc.) to refine the coarse silicon, establishing a partitioning equilibrium between the silicon and slag phases for the secondary elements. During refining, the temperature of the refining mixture is reduced from about 1900 ℃ to about 1500 ℃. To prevent the mixture from freezing, it is supplied with a reagent that is gaseous under the operating conditions, as described above. For example, the addition of oxygen results in the oxidation of silicon to silicon dioxide, and the energy released keeps the mixture in the process vessel in a liquid state. The term "oxidative refining" includes the combination of the addition of an oxygen-containing gas mixture and the addition of one or more slag formers.
When the oxidative refining is finished, the silicon phase and the slag phase, which are normally still liquid mixtures, are separated.
The main disadvantage of the conventional oxidation refining method is that silicon is lost by the presence of slag in the form of silica or metallic silicon in the slag and also that unnecessary minor elements cannot be removed effectively. This reduces the economic viability of silicon production and the quality of the corresponding product.
The object of the present invention is to improve the economic feasibility of industrial silicon production and the efficiency of removing unnecessary secondary elements, thereby improving the quality of products.
The invention provides a method for the oxidative refining of crude molten silicon in the production of industrial silicon, wherein the crude molten silicon is mixed during refining with a particulate mediator which contains a minimum of 8 mass% of metallic silicon and at least one or more of the elements H, C, O, F, Cl, Ca, Fe and Al, the mediator being described by a characteristic number K which has a value of 0.03 to 6mm-1And is calculated by:
Figure BDA0003327471950000031
wherein
d50,MIs the particle size (diameter) d at 50% of the undersize mass of the medium grading curve50,Med[mm]And an
εm,MIs the average effective porosity of the particulate mediator.
It has been surprisingly found that the addition of a characteristic number K of 0.03 to 6mm during the refining of the crude molten silicon-1The particulate media of (a) can improve the productivity of industrial silicon production and the quality of industrial silicon. The reason for this is firstly to reduce silicon loss by more efficient phase separation between silicon and slag and secondly to more efficiently remove unwanted accompanying elements. The former therefore leads to a higher yield of industrial silicon and therefore to a lower specific energy consumption for the production of industrial silicon. Another advantage of the process of the invention lies in the possibility of utilizing and/or recovering by-products and waste materials in the context of recycling economy.
The crude molten silicon is preferably produced by carbothermic reduction of quartz with coal in an electric furnace.
Oxygen of coarse molten siliconThe chemical refining is preferably carried out by treatment with a reactive gas mixture preferably comprising a compound selected from Cl2、O2、SiCl4Wet H2And CO2And combinations thereof. The reactive gas mixture is preferably diluted with an inert gas selected from the group consisting of nitrogen and argon and combinations thereof.
The technical silicon has a Si content of <99.9 mass%, based on the total weight of the technical silicon. The accompanying element is typically selected from Fe, Ca, Al, Ti, Cu, Mn, Cr, V, Ni, Mg, Co, W, Mo, As, Sb, Bi, S, Se, Te, Zr, Ge, Sn, Pb, Zn, Cd, Sr, Ba, Y, B, C, P and O.
The Si content was determined as follows: the weight fraction of accompanying elements is subtracted from 100 mass%.
An important species of industrial silicon refined in this method is silicocalcium (calcium disilicide, CaSi) having 55 to 65 mass% of Si and 35 to 45 mass% of Ca2) Ferrosilicon having 45 to 90 mass% of Si and 10 to 55 mass% of Fe, and metallurgical silicon having 98 to 99.5 mass% of Si.
The industrial silicon produced preferably has a Si content of at least 90 mass%, more preferably at least 95 mass%, more particularly at least 97 mass%.
In the oxidative refining of crude molten silicon, a mediator is added to the crude molten silicon to supplement or replace conventional slagging additives. The slagging additive is preferably selected from silica sand, limestone, quicklime, dolomite and fluorite.
In a preferred embodiment, the weight fraction of activated carbon in the mediator is at most 0.1, preferably at most 0.08, more preferably at most 0.06, more particularly at most 0.04, based on the total mass of the mediator. In the present invention, "activated carbon" is intended to mean the carbon in the mediator with O2A carbon moiety that reacts up to temperatures of 1100 ℃ and undergoes thermooxidative degradation. Activated carbon generally includes carbon in organic compounds (e.g., oils, fats, polymers) as well as carbon in inorganic compounds (e.g., carbonates, carbides) and the elemental carbon of allotropes.
According to a preferred embodiment, the water content of the mediator does not exceed 5 mass%, preferably does not exceed 3 mass%, more preferably does not exceed 1 mass%, more particularly does not exceed 1000 ppmw. According to a preferred embodiment, the oxygen weight fraction of the mediator is not more than 0.4, preferably not more than 0.3, more preferably not more than 0.2, more particularly not more than 0.15, but at least 0.01.
The minimum amount of metallic silicon in the mediator is preferably 10 mass%, more preferably at least 20 mass%, very preferably at least 30 mass%, more particularly at least 40 mass%.
The mediator preferably comprises silicon residues, preferably selected from by-products or waste from the silicon production or silicon processing industry, examples being:
silicon residues produced in the production or machining of silicon, for example polycrystalline silicon, polycrystalline silicon or monocrystalline silicon, in particular in connection with chipping, grinding and/or sawing;
silicon residues produced in the production of granular metallic silicon, for example in fluidized bed, centrifugation, gas atomization and water granulation processes;
-thermal reduction of SiO by carbon2Producing silicon residues produced in industrial grade silicon;
-silicon residues produced during mechanical processing and optionally one or more industrial silicon fractionations. The machining may more particularly involve comminution and/or grinding. Examples of typical classification processes are sieving and/or screening;
silicon residues produced in the production of silanes. These may be, for example, neutralized catalyst material from a chlorosilane reactor before and/or after recovery of Cu; more specifically, from Muller-Rochow direct synthesis operations, hydrochlorination or low temperature conversion of silanes.
Before these silicon residues are used in the mediator according to the invention, their purification is generally not necessary.
The mediator preferably comprises at least 10 mass% silicon residues, more preferably at least 20 mass%, very preferably at least 30 mass%, more particularly at least 50 mass% silicon residues.
The media are preferably subjected to a process of comminution (e.g. grinding, crushing), classification (e.g. sieving, screening) and/or agglomeration (e.g. granulation, briquetting, sintering) to obtain the desired value of the characteristic number K.
In order to determine a particularly defined value of the characteristic number K, the mediator is preferably agglomerated (for example by granulation, briquetting and/or sintering) and dried.
The elements present in the mediator together with the metallic silicon may take the form of compounds or alloys of these elements.
In addition to the elements already described, the particle mediator may also include the following companion elements: si, Li, Na, K, Mg, Ca, Ba, Ti, Zr, V, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Zn, B, Sn, Pb, N, P, As, Sb, Bi, S.
When the mediator is added, the mass ratio of the mass (mediator) to the mass (crude molten silicon) is preferably 0.01 to 0.5, more preferably 0.02 to 0.25, very preferably 0.03 to 0.15, and more particularly 0.04 to 0.1.
d50,MPreferably from 1 to 100mm, more preferably from 10 to 75mm, very preferably from 15 to 50mm, more particularly from 20 to 30 mm.
The particulate mediator preferably has an average effective porosity of from 0 to 0.6, more preferably from 0.05 to 0.4, very preferably from 0.1 to 0.35, more particularly from 0.15 to 0.3.
When the oxidizing refining is finished, the industrial silicon and slag phases, which are usually still liquid mixtures, are separated and the liquid industrial silicon solidifies on a cooled surface or in a cooled medium. This can be accomplished, for example, by decanting the mixture, pouring the floating phase of the industrial silicon into a tank, and solidifying the industrial silicon in the tank.
The liquid technical silicon can further preferably be doped or alloyed in particular with elements. This may be appropriate, for example, if the industrial silicon to be produced is intended for the synthesis of chlorosilanes. This relates to one or more elements from the group comprising Al, Cu, Sn, Zn, O and P, or compounds or two or more compounds of these elements, or mixtures of these elements and compounds.
The silicon content of the mediator can be determined, for example, by X-ray fluorescence analysis (XFA), ICP-based analysis (ICP-MS, ICP-OES) or Atomic Absorption Spectroscopy (AAS).
For mixtures of particulate matter with particle sizes mainly >0.1mm, sieve analysis is usually performed to characterize the particle mixture. The particle size distribution was determined by sieve analysis according to DIN 66165. The average particle size/diameter can be calculated from the particle size distribution according to DIN ISO 9276-2.
The total porosity of a substance consists of the sum of interconnected and interconnected voids (open porosity; in the present invention: effective porosity) and interconnected voids (closed porosity). Porosity measurements were made according to ASTM C373-88 according to Archimedes' principle. The porosity of the material can also be achieved by calculation of the absolute and apparent densities. The absolute and apparent densities can be determined by gravimetric and volumetric measurements using a gas pycnometer. The determination of the density of solids is described in DIN 66137-2: 2019-03.
Preferably, a multiphase analyzer, such as LECO RC-612 (see also DIN 19539), is used to determine the amount of "activated carbon" and the water content in the mediator.
Examples
The experiments described below were carried out at ambient air and room temperature (20 ℃).
Liquid crude silicon from a continuous process for the production of metallurgical silicon is collected in a treatment vessel and then subjected to an oxidative refining (refining gas: oxygen/air mixture [ oxygen content 30 vol% based on the total volume of the gas mixture ] with the addition of different mediators over a period of 100 minutes](ii) a Volumetric flow rate of the mixture: 16Nm of liquid crude silicon per ton3H), the silicon phase is poured into the tank and finally solidified. After cooling to room temperature and mechanical removal of the silicon from the cell, the specific energy consumption per ton of silicon product and the purity of the silicon product were determined. The experiment was analyzed in comparison to the conventional process: the specific energy consumption per ton of silicon product is usually 13.0MWh/t, and the purity of the silicon product is about 98.5%. Tables 1 and 3 provide a summary of the mediators used-the experimental results are summarized in tables 2 and 4.
TABLE 1
Figure BDA0003327471950000061
TABLE 2
Figure BDA0003327471950000071
TABLE 3
Figure BDA0003327471950000072
TABLE 4
Figure BDA0003327471950000081
The examples show that the use of mediators in the production of metallurgical silicon in the present invention is economically advantageous.

Claims (7)

1. A method of oxidatively refining crude molten silicon in the production of technical silicon, wherein the crude molten silicon is mixed during refining with a particulate mediator comprising a minimum of 8 mass% metallic silicon and comprising at least one or more of the elements H, C, O, F, Cl, Ca, Fe and Al,
the mediator is described by a characteristic number K, the value of which is between 0.03 and 6mm-1And calculated as follows:
Figure FDA0003327471940000011
wherein d is50,MIs the particle size (diameter) d at 50% of the undersize mass of the grading curve of the medium50,Med[mm]And an
εm,MIs the average effective porosity of the particulate mediator.
2. The method of claim 1, wherein the technical silicon has a Si content of at least 95 mass%.
3. The method according to one or more of the preceding claims, wherein said media comprises silicon residues selected from by-products or waste obtained in the production or machining of silicon.
4. A method according to one or more of the preceding claims, wherein the weight fraction of activated carbon in the mediator is at most 0.1, based on the total mass of the mediator, wherein "activated carbon" is the sum of O in the mediator2A carbon moiety that reacts up to temperatures of 1100 ℃ and undergoes thermooxidative degradation.
5. A method according to one or more of the preceding claims, wherein the water content of the mediator does not exceed 5 mass%.
6. A method according to one or more of the preceding claims, wherein the mediator has an oxygen weight fraction of not more than 0.4 mass%.
7. The method according to one or more of the preceding claims, wherein the mass ratio of mass (mediator) to mass (raw molten silicon) at the time of addition of the mediator is between 0.01 and 0.5.
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